Optical communication systems are known in which multiple optical signals carrying data, for example, propagate along an optical fiber from a transmitter to a receiver. In such optical communication systems, often referred to as wavelength division multiplexed (WDM) optical communication systems, each optical signal has a corresponding one of a plurality of wavelengths. In the receiver, the optical signals are filtered or demultiplexed and converted into corresponding electrical signals which also carry the data. The data is typically in digital form and thus constitutes a series of binary bits. Errors often occur during transmission of the data, such as a “1” bit may be received as a “0” bit and visa versa. In order to correct for such errors, the data is coded in the transmitter in accordance with a so-called forward error correction (FEC) code, whereby additional bytes are added to the data and then manipulated by known algorithms. The encoded data is then transmitted to the receiver, where related algorithms may be used to decode the data and correct errored bits or bytes that may be present.
FEC, however, cannot correct for an unlimited number of errors present in the data. Rather, for a given FEC code to effectively eliminate errors, the number of errors present must be below a threshold amount. In particular, the bit error rate (BER) of the data, i.e., the ratio of errored bits to total number of transmitted bits, must be below a certain value. For example, typical FEC codes used in connection with communication systems that transmit a 10 giga-bit/second data streams, require that the BER must be below 10−3 to provide adequate error correction.
Under certain circumstances, however, the BER may exceed the error correcting capability of the FEC. For example, during start-up of the WDM optical communication systems noted above, various electrical or optical components in such systems may not be properly set to process the received optical signals, thereby resulting in excessively high bit error rates, e.g., greater than 10−3, which cannot be reduced by FEC. Such high bit error rates are typically unacceptable for many telecommunication applications.
Accordingly, there is a need for an optical communication system that can reduce bit error rates to facilitate adequate forward error correction decoding.